Processes and systems for regenerating alkali process streams

ABSTRACT

Processes for regenerating alkali process streams are disclosed herein, including streams containing sodium hydroxide, magnesium hydroxide, and combinations thereof. Systems for regenerating alkali process streams are disclosed herein, including streams containing sodium hydroxide, magnesium hydroxide, and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/571,483, entitled “PROCESS AND SYSTEMS FOR REGENERATING ALKALIPROCESS STREAMS,” filed Nov. 2, 2017, which claims priority toInternational Application No. PCT/US2016/030804, entitled “PROCESSES ANDSYSTEMS FOR REGENERATING ALKALI PROCESS STREAMS,” filed May 4, 2016,which claims priority to U.S. Provisional Patent Application No.62/156,703, entitled “PROCESSES AND SYSTEMS FOR REGENERATING ALKALIPROCESS STREAMS,” filed May 4, 2015, all of which are incorporatedherein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates generally to mineral processing. Morespecifically, the present disclosure relates to processes and systemsfor regenerating alkali process streams.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments disclosed herein will become more fully apparent fromthe following description and appended claims, taken in conjunction withthe accompanying drawings. The drawings depict primarily generalizedembodiments, which embodiments will be described with additionalspecificity and detail in connection with the drawings in which:

FIG. 1 illustrates one embodiment of a process for regenerating alkalistreams.

FIG. 2 illustrates another embodiment of a process for regeneratingalkali streams.

FIG. 3 illustrates another embodiment of a process for regeneratingalkali streams.

FIG. 4 illustrates one embodiment of a system for regenerating alkalistreams.

FIG. 5 illustrates another embodiment of a system for regeneratingalkali streams.

FIG. 6 illustrates another embodiment of a system for regeneratingalkali streams.

FIG. 7 (composed of FIGS. 7A and 7B) illustrates data generated duringthe experiments of Example 1.

FIG. 8 plots data from FIG. 7 and illustrates sulfur removal.

FIG. 9 plots different data from FIG. 7 and further illustrates sulfurremoval.

FIG. 10 plots data from Table 3 and illustrates removal of calcium ionsby sodium bicarbonate.

FIG. 11 plots data from Table 4 and illustrates calcium removal bypotassium carbonate.

FIG. 12 plots data from Table 5 and illustrates calcium removal bylithium carbonate.

FIG. 13 plots data illustrating sulfur removal in the presence ofmagnesium ions.

FIG. 14 plots data illustrating pH buffering of calcium hydroxide bymagnesium ions.

DETAILED DESCRIPTION

Processes and systems for regenerating alkali process streams aredisclosed herein. The processes and systems relate to oxidation ofsulfides, in particular, metal sulfides. Oxidation of metal sulfides canbe important for recovery of metals, such as gold and silver, from rawsulfidic ores or sulfidic ore concentrates.

In some embodiments, a process for regenerating alkali streams comprisesoxidizing an ore containing a metal sulfide (e.g., as part of a sulfidicore) in an oxidizer solution, mixing alkali metal- or alkali earthmetal-containing compounds with the oxidizer solution and generating anaqueous sulfate, separating solid oxidized ore from the aqueous sulfate,and mixing lime with the aqueous sulfate, thereby forming hydroxide andsolid sulfate. The process may further comprise separating the solidsulfate from hydroxide and generating additional aqueous sulfate withthe hydroxide.

In some embodiments, a system for regenerating alkali streams comprisesan ore supply system, an oxidizing agent supply system, a pH modifiersupply system configured to supply alkali metal- or alkali earthmetal-containing compounds, and an oxidizer system in communication withthe ore supply system, the oxidizing agent supply system, and the pHmodifier supply system, the oxidizer system configured to oxidizesulfidic ore. The system may further comprise a first separation systemin communication with the oxidizer system and configured to receivesolid oxidized ore and aqueous sulfates from the oxidizer system andconfigured to separate the solid oxidized ore from the aqueous sulfates.The system may further comprise a regeneration system in communicationwith the first separation system and configured to receive at least aportion of the aqueous sulfates, the regeneration system incommunication with a lime supply system and configured to react theaqueous sulfates with calcium hydroxide, magnesium hydroxide, or bothfrom the lime supply system, and thereby form solid calcium sulfate andadditional hydroxide. The system may further comprise a secondseparation system in communication with the regeneration system andconfigured to separate the solid calcium sulfate from the additionalhydroxide and any residual calcium hydroxide or magnesium hydroxide fromthe lime supply system. The system may further comprise a recycle systemin communication with the second separation system and the pH modifiersupply system. The recycle system may be configured to direct theadditional hydroxide and any residual magnesium hydroxide from thesecond separation system to the pH modifier supply system.

The phrase “in communication with” is used in its ordinary sense, and isbroad enough to refer to any suitable coupling or other form ofinteraction between two or more entities or systems, includingmechanical, electrical, magnetic, electromagnetic, fluid, and thermalinteraction. Two components or systems may interact with each other eventhough they are not in direct contact with each other. For example, twocomponents or systems may be coupled to each other through anintermediate component or system.

FIG. 1 illustrates one embodiment of a process 1 for regenerating alkalistreams. Step 10 comprises oxidizing a sulfide. The oxidizing may beconducted at atmospheric pressure or increased pressure (such as, forexample, about 30 bar or less). The oxidation may be conducted atambient temperature or higher (such as, for example, 300° C. or less).The oxidation may be conducted under acidic or alkaline conditions.

Step 25 comprises generating an aqueous sulfate. Oxidizing the sulfidemay produce sulfuric acid. The sulfuric acid may be reacted with analkali metal- or alkali earth metal-containing compounds to generate anaqueous sulfate. The alkali metal or alkali earth metal sulfate maycomprise potassium sulfate, sodium sulfate, lithium sulfate, magnesiumsulfate, or combinations thereof. The alkali metal- or alkali earthmetal-containing compounds may comprise an alkali metal or alkali earthmetal hydroxide, such as, for example, sodium hydroxide, potassiumhydroxide, lithium hydroxide, magnesium hydroxide, or combinationsthereof. The alkali metal-containing compounds may comprise an alkalimetal or alkali earth metal carbonate, such as, for example, trisodiumhydrogendicarbonate dihydrate, sodium carbonate, sodium bicarbonate,potassium carbonate, potassium bicarbonate, lithium carbonate, lithiumbicarbonate, magnesium carbonate, or combinations thereof. The alkalimetal- or alkali earth metal-containing compounds may be used to controlthe pH of the oxidizing. Step 25 may be performed in the same reactionvessel as step 10.

Step 40 comprises mixing lime with the aqueous sulfate, thereby forminga hydroxide and a solid sulfate. The lime may comprise quicklime, slakedlime, dolomitic lime, or combinations thereof. The lime may be mixed dryor as an aqueous slurry.

As used herein, unless specified otherwise, “quicklime” refers tomaterials comprised primarily of calcium oxide (“CaO”), such asmaterials derived from the calcination of limestone or other calciumcarbonate-containing substances.

As used herein, unless specified otherwise, “slaked lime,” also known ashydrated lime, refers to materials comprised primarily of calciumhydroxide (“CaO”), such as materials derived from mixing quicklime withwater.

As used herein, unless specified otherwise, “dolomitic lime” refers tomaterials derived from the calcination of dolomite. “Dolomiticquicklime” refers to materials comprised primarily of calcium oxide andmagnesium oxide. “Slaked dolomitic lime,” also known as hydrateddolomitic lime, refers to materials comprised primarily of calciumhydroxide and magnesium hydroxide. Unless specified, “dolomitic lime”encompasses dolomitic quicklime, slake dolomitic lime, and combinationsthereof.

Step 50 comprises separating solid sulfate from hydroxide. The solidsulfate may comprise calcium sulfate or gypsum. The hydroxide may beaqueous, solid, or a combination thereof. The hydroxide may be residualhydroxide from step 25, hydroxide introduced with the lime at step 40,and/or generated by reaction with the aqueous sulfate at step 40. Forexample, solid magnesium hydroxide and aqueous sodium hydroxide may beseparated from solid calcium sulfate.

Step 60 comprises optionally removing additional calcium ions from thehydroxide. Removing calcium ions may comprise mixing carbonateion-generating compounds with the aqueous hydroxide and separating solidcalcium carbonate from the aqueous hydroxide. “Carbonate ion-generatingcompounds,” as used herein, refers to any compound that releasescarbonate ions upon solubilizing in water.

Step 70 comprises optionally generating additional aqueous sulfate withthe hydroxide (aqueous and/or solid). For example, the hydroxide of step70 may be recycled to step 25 to generate additional aqueous sulfate.

The process 1 may include steps not shown in FIG. 1. Processes with anysub-combination of the steps of FIG. 1 are also within the scope of thisdisclosure.

FIG. 2 illustrates one embodiment of a process 100 for regeneratingalkali streams. The process 100 encompasses specific embodiments of thesteps of process 1. The process 100 disclosure applies to the process 1as well, but does not limit it. In particular, the disclosure relatingto the process 100 steps applies to the process 1 steps with similarnumbers.

Step 110 of the process 100 comprises oxidizing a metal sulfide in anoxidizer solution. An example of a metal sulfide is iron sulfide(“FeS₂”), such as in pyrite and marcasite. For example, ore containingiron sulfide may comprise precious metals, such as gold and silver, inthe grain boundaries of the pyrite and/or distributed throughout thepyrite matrix. The same can be true for other sulfides, such as othermetal sulfides.

The oxidizing process may be continuous, a semi-batch process, or abatch process. The metal sulfide may be supplied to the oxidizingprocess in a number of forms, such as, by way of non-limiting example,raw ore, milled ore, flotation concentrate, and flotation tailings. Oneof ordinary skill in the art, having the benefit of this disclosure,will recognize that metal sulfide may be supplied to the oxidizingsolution in a number of forms and ways.

The oxidizing may be conducted at atmospheric pressure or increasedpressure. Non-limiting examples of increased pressure include 30 bar orless. The pressure may be supplied by a gaseous oxidizer, such as oxygengas and/or air.

The oxidizing may be conducted at ambient temperature or higher.Non-limiting examples of higher temperature include 300° C. or less.

The oxidizing may be conducted under acidic or alkaline conditions. Insome embodiments, the oxidizing may be conducted under alkalineconditions at a pH greater than about 8, greater than about 9, orgreater than about 10. Additionally, in such embodiments, the oxidationmay be conducted at about ambient temperature to about 50° C. or aboutambient temperature to about 40° C. Alternatively, or in additionthereto, in such embodiments, the oxidation may be conducted atatmospheric pressure.

Step 120 comprises mixing a sodium-containing pH modifier stream withthe oxidizer solution of step 110. The sodium-containing pH modifierstream may be used to control the pH of the oxidizer solution. Thesodium-containing pH modifier stream may comprise sodium hydroxide,trisodium hydrogendicarbonate dihydrate (such as contained in trona),sodium carbonate, sodium bicarbonate, or combinations thereof. Forexample, the sodium-containing pH modifier stream may comprise trona incombination with sodium hydroxide. The sodium hydroxide may be at leastpartially supplied by a recycle stream, as will be discussed below inrelation to step 170.

Step 110 may generate sulfuric acid during oxidation of the metalsulfide. Step 120 may in turn generate sodium sulfate from thesodium-containing compounds of the sodium-containing pH modifier streamreacting with the sulfuric acid. The sodium-containing pH modifierstream may also comprise non-sodium-containing compounds that also arepH modifiers, such as, for example, potassium hydroxide, lithiumhydroxide, potassium carbonate, potassium bicarbonate, lithiumcarbonate, lithium bicarbonate, or combinations thereof. Whennon-sodium-containing compounds are also present, then in addition tosodium sulfate being generated, other alkali metal sulfates may also begenerated and mixed with the aqueous sodium sulfate.

Step 130 comprises separating a solid oxidized ore stream containingmetal oxides and an aqueous sodium sulfate stream from the oxidizersolution of step 120. Separation may be accomplished using a variety ofsolid-liquid separation equipment and technologies. For example,thickeners and filters may be used to separate the solid oxidized orestream from the aqueous sodium sulfate stream. One of ordinary skill inthe art, having the benefit of this disclosure, will recognize that thesolid-liquid separation may be accomplished a number of ways.

The solid oxidized ore stream may undergo further processing. Forexample, the solid oxidized ore stream may undergo a cyanide leachprocess to remove precious metals from the solid metal oxide. In thatexample, the solid metal oxide may be heaped onto leach pads. One ofordinary skill in the art, having the benefit of this disclosure, willrecognize that the solid oxidized ore stream may be further processed ina number of ways.

Step 140 comprises mixing lime with the aqueous sodium sulfate stream,thereby forming sodium hydroxide and calcium sulfate. The chemicalreactions may be represented as:Ca(OH)₂+Na₂SO₄→CaSO_(4(s))+2NaOH_((aq))

The lime may comprise quicklime, slaked lime, dolomitic quicklime,dolomitic slaked lime, or combinations thereof. Mixing lime with theaqueous sodium sulfate stream may comprise mixing a lime slurry with theaqueous sodium sulfate stream. When the lime comprises dolomitic lime,it may be desirable to maintain a pH of about 8 to about 9 while mixing.

The calcium sulfate may comprise gypsum.

In some embodiments, the aqueous sodium sulfate stream, prior to mixinglime therewith, has a neutral pH or an acidic pH. In other embodiments,the aqueous sodium sulfate stream has an alkaline pH, prior to mixinglime therewith.

Step 150 comprises separating a solid calcium sulfate stream from anaqueous sodium hydroxide stream. The separation may be accomplishedusing a variety of solid-liquid separation equipment and technologies.For example, thickeners, filters, hydrocyclones, centrifuges, andmembranes may be used to separate the solid calcium sulfate stream fromthe aqueous sodium hydroxide stream. One of ordinary skill in the art,having the benefit of this disclosure, will recognize that thesolid-liquid separation may be accomplished a number of ways.

When the lime in step 140 comprises dolomitic lime, a suspension ofmagnesium hydroxide may be maintained in the aqueous sodium hydroxidestream while separating the solid calcium sulfate stream therefrom.Alternatively, the magnesium hydroxide may be removed with the solidcalcium sulfate.

Step 160 comprises optionally removing calcium ions from the aqueoussodium hydroxide stream. Removing calcium ions from the aqueous sodiumhydroxide stream may comprise mixing carbonate ion-generating compoundswith the aqueous sodium hydroxide stream and separating a solid calciumcarbonate stream from the aqueous sodium hydroxide stream. Examples ofcarbonate ion-generating compounds include sodium carbonate, sodiumbicarbonate, and trisodium hydrogendicarbonate dihydrate (such ascontained in trona). Additionally or alternatively,non-sodium-containing carbonate ion-generating compounds may be used aswell, such as, for example, potassium carbonate, potassium bicarbonate,lithium carbonate, and lithium bicarbonate.

Step 160 may further comprise seeding the aqueous sodium hydroxidestream with calcium carbonate crystals. This may increase the size ofcalcium carbonate crystals formed, which may make filtration and solidsremoval easier.

Step 170 comprises optionally mixing the aqueous sodium hydroxide streamwith the sodium-containing pH modifier stream. Step 170 may be performedin addition to step 160, without step 160, before step 160, orsimultaneously with step 160.

Steps 160 and 170 may be performed a number of ways. For example, thesodium-containing pH modifier stream may comprise carbonateion-generating compounds, such as from trona. A portion of thesodium-containing pH modifier stream (or a supply source thereof) may bemixed with the aqueous sodium hydroxide stream to provide the necessarycarbonate ion-generating compounds. In this example, step 160 could beperformed prior to step 170.

In another example, all of the sodium-containing pH modifier stream maybe mixed with the aqueous sodium hydroxide stream, prior to step 120. Inthis example, steps 160 and 170 could be performed simultaneously. Thiscould effectively purify and/or enhance the sodium-containing pHmodifier stream. For example, when trona is used in thesodium-containing pH modifier stream, insoluble solids and inorganicspresent in the trona could be removed along with the calcium carbonate,purifying the trona. Additionally, sodium carbonate components of thetrona can be reacted with calcium ions to form solid calcium carbonate.A representation of the chemical reaction is as follows:Ca(OH)₂+Na₂CO₃→2NaOH+CaCO_(3(s))Sodium bicarbonate may be used. Sodium carbonate may be more efficaciousat modifying pH than the sodium bicarbonate. Therefore, increasing theconcentration of sodium carbonate may enhance the sodium-containing pHmodifying stream in this example.

Additionally, step 160 and/or step 170 may be performed prior to orsimultaneously with step 150. For example, after step 140, step 170 maybe performed with the sodium-containing pH modifier stream supplyingcarbonate ion-generating compounds. Solid calcium carbonate could thenbe separated from the aqueous sodium hydroxide stream at the same timeas the solid calcium sulfate (i.e., step 160 performed at the same timeas step 150). In this example, steps 150, 160, and 170 would beperformed prior to step 120 (i.e., prior to mixing the sodium-containingpH modifier stream with the oxidizer solution).

In some embodiments, instead of performing optional step 170, all or aportion of the aqueous sodium hydroxide stream is not mixed with thesodium-containing pH modifier stream. Instead, all or a portion of theaqueous sodium hydroxide stream is used in a different process, such asa process related to the recovery of precious metals, but notspecifically involved in the oxidation of sulfides.

One of ordinary skill in the art, having the benefit of this disclosure,will recognize that the steps of the process 100 may be performednon-sequentially and in a number of different orders. Additionally, theprocess 100 may include steps not shown in FIG. 2. Processes with anysub-combination of the steps of FIG. 2 are also within the scope of thisdisclosure.

FIG. 3 illustrates one embodiment of a process 200 for regeneratingalkali streams. The process 200 encompasses specific embodiments of thesteps of the process 1. The process 200 disclosure applies to theprocess 1 as well, but does not limit it. In particular, the disclosurerelating to the process 200 steps applies to the process 1 steps withsimilar numbers. Likewise, similar disclosure in the process 100 appliesto the process 200, but does not limit it.

Step 210 of the process 200 comprises oxidizing a metal sulfide in anoxidizer solution. As with step 110 of the process 100, the oxidizingprocess may be continuous, a semi-batch process, or a batch process. Theoxidizing may be conducted at atmospheric pressure or increasedpressure. The oxidizing may be conducted at ambient temperature orhigher. The oxidizing may be conducted under acidic or alkalineconditions.

Step 220 comprises mixing a magnesium-containing pH modifier stream withthe oxidizer solution of step 210. The magnesium-containing pH modifierstream may be used to control the pH of the oxidizer solution. Themagnesium-containing pH modifier stream may comprise, for example,magnesium hydroxide, magnesium carbonate, or combinations thereof. Themagnesium hydroxide may be at least partially supplied by a recyclestream, as will be discussed below in relation to step 270.

Step 210 may generate sulfuric acid during oxidation of the metalsulfide. Step 220 may in turn generate magnesium sulfate from themagnesium-containing compounds of the magnesium-containing pH modifierstream reacting with the sulfuric acid. The magnesium-containing pHmodifier stream may also comprise non-magnesium-containing compoundsthat also are pH modifiers, such as, for example, trona, sodiumhydroxide, potassium hydroxide, lithium hydroxide, potassium carbonate,potassium bicarbonate, lithium carbonate, lithium bicarbonate, orcombinations thereof. When non-magnesium-containing compounds are alsopresent, then in addition to magnesium sulfate being generated, otheralkali metal and alkali earth metal sulfates may also be generated andmixed with the aqueous magnesium sulfate.

Step 230 comprises separating a solid oxidized ore stream containingmetal oxides and an aqueous magnesium sulfate stream from the oxidizersolution of step 220. Separation may be accomplished using a variety ofsolid-liquid separation equipment and technologies, as discussed in step130 of the process 100. Additionally, the solid oxidized ore stream mayundergo further processing as discussed in the process 100.

Step 240 comprises mixing lime with the aqueous magnesium sulfatestream, and magnesium hydroxide and calcium sulfate would thereby beformed. The lime may comprise quicklime, slaked lime, dolomiticquicklime, dolomitic slaked lime, or combinations thereof. Mixing limewith the aqueous magnesium sulfate stream may comprise mixing a limeslurry with the aqueous magnesium sulfate stream. The calcium sulfatemay comprise gypsum.

In some embodiments, the aqueous magnesium sulfate stream, prior tomixing lime therewith, has a neutral pH or an acidic pH. In otherembodiments, the magnesium sulfate stream has an alkaline pH, prior tomixing lime therewith.

Step 250 comprises separating a solid calcium sulfate stream from asolid magnesium hydroxide stream. The separation may be accomplishedusing a variety of solid-solid separation equipment and technologies,such as, for example, filters, sieves, hydrocyclones, centrifuges, andmembranes. One of ordinary skill in the art, having the benefit of thisdisclosure, will recognize that the solid-solid separation may beaccomplished a number of ways.

When the lime in step 240 comprises dolomitic lime, a suspension ofmagnesium hydroxide may be maintained in an aqueous stream whileseparating the solid calcium sulfate stream therefrom. Alternatively,the magnesium hydroxide may be removed with the solid calcium sulfateand later separated.

Step 260 comprises optionally removing calcium ions from the aqueoushydroxide stream. The aqueous hydroxide stream may comprise aqueoussodium hydroxide as well as aqueous magnesium hydroxide, if sodium ionsare present earlier in the process. Removing calcium ions from theaqueous hydroxide stream may comprise mixing carbonate ion-generatingcompounds with the aqueous hydroxide stream and separating a solidcalcium carbonate stream from the aqueous hydroxide stream. Examples ofcarbonate ion-generating compounds include sodium carbonate, sodiumbicarbonate, and trisodium hydrogendicarbonate dihydrate (such ascontained in trona). Additionally or alternatively,non-sodium-containing carbonate ion-generating compounds may be used aswell, such as, for example, potassium carbonate, potassium bicarbonate,lithium carbonate, and lithium bicarbonate.

Step 260 may further comprise seeding the aqueous hydroxide stream withcalcium carbonate crystals. This may increase the size of calciumcarbonate crystals formed, which may make filtration and solidsremoval/separation easier.

Step 270 comprises optionally mixing the aqueous hydroxide stream andthe solid magnesium hydroxide stream with the magnesium-containing pHmodifier stream. Step 270 may be performed in addition to step 260,without step 260, before step 260, or simultaneously with step 260.

Steps 260 and 270 may be performed a number of ways. For example, themagnesium-containing pH modifier stream may comprise carbonateion-generating compounds, such as from trona. A portion of themagnesium-containing pH modifier stream (or a supply source thereof) maybe mixed with the aqueous hydroxide stream to provide the necessarycarbonate ion-generating compounds. In this example, step 260 could beperformed prior to step 270.

In some embodiments, instead of performing optional step 270, all or aportion of the aqueous hydroxide stream is not mixed with themagnesium-containing pH modifier stream. Instead, all or a portion ofthe aqueous hydroxide stream is used in a different process, such as aprocess related to the recovery of precious metals, but not specificallyinvolved in the oxidation of sulfides. Likewise, the same alternativesapply to use of the solid magnesium hydroxide stream.

One of ordinary skill in the art, having the benefit of this disclosure,will recognize that the steps of the process 200 may be performednon-sequentially and in a number of different orders. Additionally, theprocess 200 may include steps not shown in FIG. 3. Processes with anysub-combination of the steps of FIG. 3 are also within the scope of thisdisclosure.

FIG. 4 illustrates one embodiment of a system 200 for regeneratingalkali streams. The system 200 encompasses specific embodiments of theprocess 100. The system 200 disclosure applies to the process 100 aswell, but does not limit it.

The system 200 comprises an oxidizer system 210 in communication with anore supply system 220, an oxidizing agent supply system 230, and a pHmodifier supply system 240. The oxidizer system 210 may be configured tooxidize sulfidic ore. The oxidizer system 210 may comprise an oxidizervessel. The oxidizer vessel may be configured to operate under alkalineor acidic conditions. For example, the oxidizer vessel may be configuredto operate under alkaline conditions at a pH greater than about 8,greater than about 9, or greater than about 10.

The oxidizer vessel may be configured to operate at a variety oftemperatures. The oxidizer vessel may be configured to operate at aboutambient temperatures or higher (e.g., about 10° C. to about 300° C.). Insome embodiments, the oxidizer vessel may be configured to operate atabout 20° C. to about 80° C., such as about 20° C. to about 50° C.

The oxidizer vessel may be configured to operate at a variety ofpressures. The oxidizer vessel may be configured to operate at aboutambient pressure or higher (e.g., about 1 bar to about 30 bar).

The ore supply system 220 comprises an ore feed 221 configured to supplyore to the oxidizer system 210. The ore feed 221 may be configured tosupply ore in a number of forms, such as, by way of non-limitingexample, raw ore, milled ore, flotation concentrate, and flotationtailings. One of ordinary skill in the art, having the benefit of thisdisclosure, will recognize that the ore feed 221 may be configured tooperate in a number of forms and ways.

The oxidizing agent supply system 230 comprises an oxidizing agent feed231 configured to supply oxidizing agent to the oxidizer system 210. Theoxidizing agent feed 231 may be configured to supply oxidizing agents ina number of forms, such as, by way of non-limiting example, a gas. Forexample, the oxidizing agent feed 231 may be configured to supply oxygengas, air, or combinations thereof. One of ordinary skill in the art,having the benefit of this disclosure, will recognize that the oxidizingagent feed 231 may be configured to supply oxidizing agents in a numberof forms and ways.

The oxidizing agent supply system 230 may be configured to operate atatmospheric pressure or higher. For example, the oxidizing agent feed231 may be configured to pressurize the oxidizer system 210 with oxygenand/or air gas. Alternatively, the oxidizing agent feed 231 may beconfigured to supply oxygen and/or air gas at about atmosphericpressure.

The pH modifier supply system 240 comprises a pH modifier feed 241configured to supply sodium-containing pH modifier to the oxidizersystem 210. The sodium-containing pH modifier may comprise, by way ofnon-limiting example, sodium hydroxide, trisodium hydrogendicarbonatedihydrate (such as contained in trona), sodium carbonate, sodiumbicarbonate, or combinations thereof. For example, the sodium-containingpH modifier stream may comprise trona in combination with sodiumhydroxide. The sodium hydroxide may be at least partially supplied by arecycle stream, as will be discussed below in relation to a regenerationsystem 260.

The pH modifier feed 241 may be configured to supply the pH modifier ina number of forms, such as, by way of non-limiting example, in powderform or as aqueous solution or suspension. One of ordinary skill in theart, having the benefit of this disclosure, will recognize that the pHmodifier feed 241 may be configured to operate in a number of forms andways.

The oxidizer system 210 comprises an oxidized product stream 211. Theoxidized product stream 211 is configured to convey oxidized ore andaqueous sodium sulfates away from the oxidizer vessel.

A first separation system 250 is configured to receive oxidized productstream 211 and is configured to separate solid oxidized ore from liquidaqueous sodium sulfates. The first separation system 250 may comprise asettling tank, a thickener, hydrocyclone, a filter (such as a vacuumfilter), or other solid-liquid separation equipment, alone or incombination. One of ordinary skill in the art, having the benefit ofthis disclosure, will recognize that the first separation system 250 mayinvolve a number of different separation technologies.

The first separation system 250 comprises an oxidized ore stream 251configured to convey solid oxidized ore. “Oxidized ore,” as used herein,refers to ore that contains oxidized compounds, such as metal sulfidesoxidized to metal oxides. The oxidized ore stream 251 may be configuredto convey the oxidized ore to other locations for further processing.Examples of further processing are discussed above in relation toprocess 100 and the solid metal oxide of step 130.

The first separation system 250 comprises a liquid stream 252 configuredto convey liquids separated from the oxidized ore. The liquid stream 252is configured to convey liquids comprising aqueous sodium sulfate to theregeneration system 260. An optional liquid recycle stream 253 divergesfrom the liquid stream 252 and is configured to return a portion of theliquids back to the oxidizer system 210. The liquid recycle stream 253may not be present, in which case, all of the liquids are conveyed tothe regeneration system 260.

The regeneration system 260 is in communication with a lime supplysystem 270. The regeneration system 260 is configured to react aqueoussodium sulfates with calcium hydroxide and thereby form solid calciumsulfate and aqueous sodium hydroxide (see, for example, step 140 of theprocess 100 discussed above). The regeneration system 260 may comprise aregeneration vessel configured to mix lime with the aqueous sodiumsulfate. For example, the regeneration vessel may comprise static oractive mixers. The regeneration vessel may be configured to maintain aspecific pH, such as, for example, about 10 to about 11, such as whendolomitic lime is used, or about 12 to about 13, such as whenhigh-calcium lime is used.

The lime supply system 270 comprises a lime feed 271. The lime feed 271may be configured to supply solid lime or aqueous lime. The lime feed271 may be configured to convey quicklime, slaked lime, dolomitic lime,or combinations thereof. Of course, in an aqueous slurry, any calciumoxide would react with water to form calcium hydroxide. Magnesium oxide,in an aqueous slurry, may eventually be converted to magnesiumhydroxide, depending on the amount of time the magnesium oxide particlesare exposed to water and the temperature and pressure conditions.

The regeneration system 260 comprises a regenerated product stream 261configured to convey aqueous sodium hydroxide and solid calcium sulfatesto a second separation system 280. The second separation system 280 isconfigured to separate the solid calcium sulfate from the aqueous sodiumhydroxide. The second separation system 280 comprises a solid stream 281and a liquid stream 282. The solid stream 281 is configured to conveysolids that have been separated out. The solids will comprise calciumsulfate, such as gypsum. The solid calcium sulfate may be disposed of,sold, further processed, or handled in some other way. A portion of thecalcium sulfate solids in solid stream 281 can be optionally recycledback to the regeneration system 260 as seeds so that larger calciumsulfate crystals can be grown. This could enhance the solid-liquidseparation in the second separation system 280. The liquid stream 282 isconfigured to convey separated liquids to a calcium removal system 290.The second separation system 280 may comprise thickeners, clarifiers,filters, hydrocyclones, centrifuges, and membranes, alone or incombination. One of ordinary skill in the art, having the benefit ofthis disclosure, will recognize that the solid-liquid separation may beaccomplished a number of ways.

The calcium removal system 290 may comprise a calcium removal vesselconfigured to mix carbonate ion-generating compounds with aqueous sodiumhydroxide and precipitate calcium carbonate out of the liquid, therebypurifying the aqueous sodium hydroxide (see, for example, step 160 ofthe process 100 discussed above). The calcium removal vessel maycomprise static or active mixers. The calcium removal system 290 may beconfigured to seed the calcium removal vessel with calcium carbonatecrystals. This could enhance the solid-liquid separation in the calciumremoval system 290.

The calcium removal system 290 comprises a carbonate supply 291 and acarbonate feed 292. The carbonate supply 291 may be configured to supplycarbonate ion-generating compounds, such as, for example, sodiumcarbonate, sodium bicarbonate, trisodium hydrogendicarbonate dihydrate(such as contained in trona), or combinations thereof. The carbonatesupply 291 may be supplied from a separate source or may be suppliedfrom the pH modifier supply system 240. For example, when the pHmodifier supply system 240 is configured to only supply sodiumhydroxide, then a separate source of carbonate ion-generating compoundsis required for the carbonate supply 291. However, when the pH modifiersupply system 240 is configured to at least partially supply carbonateion-generating compounds, then the carbonate supply 291 may be suppliedby the pH modifier supply system 240 (such as via the pH modifier feed241).

The calcium removal system 290 comprises a product stream 293 configuredto convey precipitated calcium carbonate and aqueous sodium hydroxide toa third separation system 295.

The third separation system 295 is configured to separate solid calciumcarbonate from the aqueous sodium hydroxide. The disclosure hereinregarding other solid-liquid separations applies to the third separationsystem 295 as well. The third separation system 295 comprises a purifiedliquid stream 296 and a solid stream 297. The purified liquid stream 296is configured to convey purified aqueous sodium hydroxide to the pHmodifier supply system 240, which may in turn reuse the sodiumhydroxide. At steady-state operation of the system 200, the purifiedliquid stream 296 is a recycle stream. The solid stream 297 isconfigured to convey solids that have been separated out. The solidswill comprise calcium carbonate. A portion of the solid stream 297 maybe mixed with the carbonate supply 291 and recycled as calcium carbonateseed. The solid calcium carbonate may be disposed of, sold, furtherprocessed, or handled in some other way.

In some embodiments, the second separation system 280 is not present andthe regenerated product stream 261 feeds directly into the calciumremoval system 290. In that embodiment, solid calcium sulfate isseparated along with solid calcium carbonate by the third separationsystem 295.

In some embodiments, the second separation system 280 and/or the thirdseparation system 295 are configured to maintain magnesium hydroxidesolids suspended in the aqueous sodium hydroxide stream while separatingout other solids, including calcium sulfate and calcium carbonate. Forexample, one or both of the separation systems may comprise ahydrocyclone or centrifuge configured, structured, and located tomaintain magnesium hydroxide solids suspended in the aqueous sodiumhydroxide stream while separating out other solids.

In some embodiments, the regeneration system 260 and the secondseparation system 280 are combined into a single unit operation, suchthat solids are removed as they are precipitated out of solution. Forexample, depending on the process conditions of the regeneration system260, it may be desirable to extract calcium sulfate as it isprecipitated to favor progress of the reaction towards calcium sulfategeneration. This may be beneficial when the calcium hydroxide ismaintained in solution.

In some embodiments, the lime feed 271 supplies finely divided lime(either as a slurry or as a powder) to the regeneration system 260. Insuch embodiments, the calcium hydroxide in the lime may not fullydissolve. Therefore, both solid calcium hydroxide and solid calciumsulfate may be present in the regeneration system 260. In thatsituation, the process conditions may be controlled to drive productionof large calcium sulfate particles (relative to the size of the suppliedcalcium hydroxide particles), such as via the seed process disclosedabove. The second separation system 280 (or an additional intermediateseparation system) may then be configured to separate primarily calciumhydroxide particles from the generally larger calcium sulfate particles.The separated calcium hydroxide particles may then be recycled back tothe regeneration system 260 and the calcium sulfate particles furtherprocessed, used for seeding, and/or disposed of.

In some embodiments, the calcium removal system 290 and the thirdseparation system 295 are combined into a single unit operation.Furthermore, in some embodiments, the regeneration system 260, thesecond separation system 280, the calcium removal system 290, and thethird separation system 295 are all combined into a single unitoperation. One of ordinary skill in the art, having the benefit of thisdisclosure, will recognize that a number of modifications may be made tothe system 200.

FIG. 5 illustrates one embodiment of a system 300 for regeneratingalkali streams. The system 300 encompasses a variation of the system200.

The system 300 does not have an equivalent to the carbonate feed stream291 of the system 200. Instead, a pH modifier feed 341 is configured todirectly feed to a calcium removal system 390, instead of feedingdirectly to the oxidizer system 210. In the system 300, the entire pHmodifier supplied by a pH modifier supply system 340 is directed to thecalcium removal system 390. Additionally, the pH modifier feed 341 isconfigured to convey carbonate ion-generating compounds, instead ofoptionally so, as in the system 200.

The calcium removal system 390 may purify and enhance the pH modifierfeed 341. For example, when trona is at least a partial source of the pHmodifier, insoluble inorganics present in the trona could be removed,thereby purifying the trona. Likewise, as calcium is removed from theaqueous sodium hydroxide stream (see, for example, step 160 of theprocess 100 discussed above) by reaction with sodium bicarbonate, thesodium carbonate content is increased, thereby enhancing the trona. Athird separation system 395 comprises a purified liquid stream 396 and asolid stream 397, as in the system 200. However, the purified liquidstream 396 directly feeds into an oxidizer system 310, instead ofindirectly via the pH modifier supply system 340, as in the system 200.

At steady-state, the mass flowrate of the purified liquid stream 396will likely be greater than the mass flowrate of the pH modifier feed341 due to addition from a lime feed 371. The purified liquid stream 396will include recycled aqueous sodium hydroxide.

Unless specifically differentiated, the above disclosure regarding thesystem 200 components and systems applies to the system 300 componentsand systems with like numbers.

FIG. 6 illustrates one embodiment of a system 400 for regeneratingalkali streams. The system 400 encompasses specific embodiments of theprocess 200. The system 400 disclosure applies to process 200 as well,but does not limit it.

The system 400 comprises an oxidizer system 410 in communication with anore supply system 420, an oxidizing agent supply system 430, and a pHmodifier supply system 440. The oxidizer system 410 may be configured tooxidize sulfidic ore. The ore supply system 420 comprises an ore feed421 configured to supply ore to the oxidizer system 410. The oxidizingagent supply system 430 comprises an oxidizing agent feed 431 configuredto supply oxidizing agent to the oxidizer system 410. The pH modifiersupply system 440 comprises a pH modifier feed 441 configured to supplya pH modifier to the oxidizer system 410. The above disclosure regardingstructural features of the system 200 applies equally to the oxidizersystem 410, the ore supply system 420, the oxidizing agent supply system430, and the pH modifier supply system 440.

In the system 200 and the system 300, magnesium hydroxide may optionallybe present in the pH modifier. By contrast, the system 400 requires thepresence of magnesium hydroxide (or oxide) in the pH modifier. The pHmodifier of the system 400 may optionally include sodium-containing pHmodifiers such as sodium hydroxide, trisodium hydrogendicarbonatedihydrate (such as contained in trona), sodium carbonate, sodiumbicarbonate, or combinations thereof. The magnesium hydroxide may be atleast partially supplied by a recycle stream, as will be discussed belowin relation to a regeneration system 460. The magnesium hydroxide (oroxide) reacts with sulfuric acid (generated by oxidation) to formaqueous magnesium sulfate.

In the system 400, an oxidized product stream 411 is configured toconvey oxidized ore and aqueous sulfates away from the oxidizer vessel.In the system 400, the aqueous sulfates include magnesium sulfates andmay include sodium sulfates.

A first separation system 450 is configured to receive the oxidizedproduct stream 411 and is configured to separate solid oxidized ore fromliquid aqueous sulfates. The first separation system 450 comprises anoxidized ore stream 451 configured to convey solid oxidized ore. Thefirst separation system 450 comprises a liquid stream 452 configured toconvey liquids separated from the oxidized ore. The liquid stream 452 isconfigured to convey liquids comprising aqueous sulfate to theregeneration system 460. An optional liquid recycle stream 453 divergesfrom the liquid stream 452 and is configured to return a portion of theliquids back to the oxidizer system 410. The liquid recycle stream 453may not be present, in which case, all of the liquids are conveyed tothe regeneration system 460. The above disclosure regarding potentialstructural features of the first separation system 250 applies equallyto the first separation system 450.

The regeneration system 460 is in communication with a lime supplysystem 470. The regeneration system 460 is configured to react aqueoussulfates with dolomitic lime and thereby form solid sulfate andhydroxide. The above disclosure regarding potential structural featuresof the regeneration system 260 applies equally to the regenerationsystem 460.

The lime supply system 470 comprises a lime feed 471. The lime feed 471may be configured to supply solid lime or aqueous lime. The lime feed271 will generally be configured to supply dolomitic lime. The dolomiticlime, whether quicklime or slaked, often has a calcium-to-magnesiumweight ratio of about 5:3.

In contrast to the system 200 that, in certain embodiments, canregenerate sodium hydroxide, the system 400, in certain embodiments, canregenerate primarily magnesium hydroxide. For example, calcium hydroxidein the dolomitic lime may react with magnesium sulfate according to thefollowing generalized reaction.Ca(OH)₂+MgSO_(4(aq))→CaSO_(4(s))+Mg(OH)_(2(s))

Once the magnesium sulfate is consumed the pH may go up, if excesscalcium hydroxide is present. If sodium sulfate is also present (such asif a sodium-containing pH modifier were present in the pH modifier feed441), then the following generalized reaction may also occur, dependingon the process conditions.Ca(OH)₂+Na₂SO₄→CaSO_(4(s))+2NaOH_((aq))

Removal of calcium sulfate from the regeneration system 460 mayfacilitate progress of the reaction. Separation of solid calciumhydroxide from solid calcium sulfate (as disclosed above) may bedesirable. Likewise, with the magnesium sulfate consumed, if excesscalcium hydroxide is present and sodium carbonate is present (such as iftrona were present in the pH modifier feed 441), then the followinggeneralized reaction may also occur.Ca(OH)₂+Na₂CO_(3(aq))→2NaOH_((aq))+CaCO_(3(s))

Depending on the pH of liquor in the regeneration system 460, themagnesium hydroxide (and oxide) introduced to the regeneration system460 as part of the dolomitic lime may be partially reacted in theregeneration system 460. This may lead to a buildup of magnesiumhydroxide in the system 400. This will be discussed more below. Toachieve more complete consumption of the magnesium sulfate, it may bebeneficial to operate the regeneration system 460 as a batch orsemi-batch process.

The regeneration system 460 comprises a regenerated product stream 461configured to convey aqueous magnesium hydroxide and solid calciumsulfates (and solid calcium carbonates if present) to a secondseparation system 480. The second separation system 480 is configured toseparate the solid calcium sulfate from the aqueous magnesium hydroxide.The second separation system 480 comprises a solid stream 481 and aliquid stream 482. The solid stream 481 is configured to convey solidsthat have been separated out. The solids may comprise calcium sulfate,such as gypsum. The solid calcium sulfate may be disposed of, sold,further processed, or handled in some other way. The liquid stream 482is configured to convey separated liquids to an optional calcium removalsystem 490. The above disclosure regarding potential structural featuresof the second separation system 280 applies equally to the secondseparation system 480.

The optional calcium removal system 490 may comprise a calcium removalvessel configured to mix carbonate ion-generating compounds with aqueousmagnesium hydroxide (and sodium hydroxide if present) and precipitatecalcium carbonate out of the liquid, thereby purifying the aqueousmagnesium hydroxide.Ca²+Na₂CO₃→2Na⁺+CaCO_(3(s))The above disclosure regarding potential structural features of thecalcium removal system 290 applies equally to the calcium removal system490.

The calcium removal system 490 comprises a carbonate supply 491 and acarbonate feed 492. The carbonate supply 491 may be configured to supplycarbonate ion-generating compounds, such as, for example, sodiumcarbonate, sodium bicarbonate, trisodium hydrogendicarbonate dihydrate(such as contained in trona), or combinations thereof. The carbonatesupply 491 may be supplied from a separate source or may be suppliedfrom the pH modifier supply system 440. For example, when the pHmodifier supply system 440 is configured to only supply magnesiumhydroxide, then a separate source of carbonate ion-generating compoundsis required for the carbonate supply 491. However, when the pH modifiersupply system 440 is configured to at least partially supply carbonateion-generating compounds, then the carbonate supply 491 may be suppliedby the pH modifier supply system 440 (such as via the pH modifier feed441).

The calcium removal system 490 comprises a product stream 493 configuredto convey precipitated calcium carbonate and aqueous magnesium hydroxideand sodium hydroxide to a third separation system 495.

The third separation system 495 (which may not be present if the calciumremoval system 490 is not present) is configured to separate solidcalcium carbonate from the aqueous magnesium hydroxide and sodiumhydroxide. The disclosure herein regarding structural features of theother solid-liquid separations applies to the third separation system495 as well. The third separation system 495 comprises a purified liquidstream 496 and a solid stream 497. The purified liquid stream 496 isconfigured to convey purified aqueous magnesium hydroxide and sodiumhydroxide to the pH modifier supply system 440, which may in turn reusethe hydroxides.

At steady-state operation of the system 400, the purified liquid stream496 is both a recycle stream and source of input of fresh magnesiumhydroxide for the oxidizer system 410. The solid stream 497 isconfigured to convey solids that have been separated out. The solids maycomprise calcium carbonate. A portion of the solid stream 497 may bemixed with the carbonate supply 491 and recycled as calcium carbonateseed. The solid calcium carbonate may be disposed of, sold, furtherprocessed, or handled in some other way.

One of the benefits of the system 400 is that magnesium hydroxide(and/or oxide) is circulated for use as a pH modifier, and may primarilybe the pH modifier. This may have oxidation benefits over primarilysodium-containing pH modifiers.

In some embodiments where magnesium hydroxide is primarily the pHmodifier, prior to steady-state operation, it may be beneficial toinitially use a sodium-containing pH modifier, such as a trona or sodiumhydroxide. During startup, when magnesium hydroxide has not yet beenintroduced into the system via the dolomitic lime, the sodium-containingpH modifier can be used to generate sodium sulfates. As the dolomiticlime and sodium sulfates react in the regeneration system 460, thenmagnesium hydroxide is introduced to the system. As magnesium hydroxidebuilds up in the system (from fresh dolomitic lime and regeneration frommagnesium sulfate), then the introduction of the sodium-containing pHmodifier can be reduced and/or eliminated.

In some embodiments, during steady-state operation, magnesium hydroxidewill buildup in the system as a result of inputs from fresh dolomiticlime and as a result of regeneration from magnesium sulfate. Oneapproach is to prevent the buildup by continuously removing magnesiumhydroxide, such as solid magnesium hydroxide, from the system. Forexample, one of the existing or additional separation systems may beused to separate solid magnesium hydroxide from the aqueous magnesiumhydroxide (and sodium hydroxide, if present). Likewise, another approachis to remove magnesium hydroxide (either aqueous or solid) from thesystem at particular concentration limits.

Another approach is to switch to primarily high-calcium lime in the limefeed 471 after the desired magnesium hydroxide concentration has beenachieved. For example, once the desired magnesium hydroxideconcentration has been achieved, then slaked lime comprising primarilycalcium hydroxide can be used. The calcium hydroxide would regeneratethe magnesium hydroxide. Make-up dolomitic lime could continue to beincorporated with the slaked lime as needed.

In some embodiments, the calcium removal system 490 and the thirdseparation system 495 are not present. Instead, after the magnesiumsulfate has been largely consumed in the reaction vessel of theregeneration system 460, carbonate ion-generating compounds can beintroduced to consume the remaining calcium ions and generate solidcalcium carbonate. The solid calcium carbonate can then be removed withthe solid calcium sulfate.

In some embodiments, the second separation system 480 and/or the thirdseparation system 495 are configured to maintain magnesium hydroxidesolids suspended in the aqueous magnesium hydroxide (and aqueous sodiumhydroxide, if present) stream while separating out other solids,including calcium sulfate and calcium carbonate. For example, one orboth of the separation systems may comprise a hydrocyclone or centrifugeconfigured, structured, and located to maintain magnesium hydroxidesolids suspended in the aqueous hydroxide stream while separating outother solids.

In some embodiments, the calcium removal system 490 and the thirdseparation system 495 are combined into a single unit operation.Furthermore, in some embodiments, the regeneration system 460, thesecond separation system 480, the calcium removal system 490, and thethird separation system 495 are all combined into a single unitoperation. One of ordinary skill in the art, having the benefit of thisdisclosure, will recognize that a number of modifications may be made tothe system 400.

EXAMPLES

Equipment and Reagent List:

ICP Spectrometer; Perkin Elmer 7300V

pH Meter; Orion 920A+

Syringe Filters; 0.45 pm

Transfer Pipet; 5 mL tip

Liquid Calibration standards Ca, Mg, Na and S; 1000 ppm

Magnesium Sulfate (Epsom Salt)

Sodium Sulfate; Reagent Grade

Sodium Bicarbonate (Arm & Hammer® baking soda)

High-Calcium Quicklime—Obtained from Cricket Mountain Lime Plant, Delta,Utah.

Dolomitic Quicklime—Obtained from Cricket Mountain Lime Plant, Delta,Utah.

Chemical Analysis of Quicklimes Used:

TABLE 1 Sample CaO MgO Fe₂O₃ Al₂O₃ SrO MnO SiO₂ BaO K₂O Na₂O P₂O₅ TiO₂ICP Type (%) (%) (%) (%) (ppm) (ppm) (%) (ppm) (ppm) (ppm) (ppm) (ppm)Total High- 93.95 1.46 0.19 0.42 604 58 1.54 18 531 276 <100 187 97.7Calcium Quicklime Dolomitic 57.94 40.00 0.37 0.18 68 558 0.50 7 94 105<100 106 98.7 Quicklime

Example 1

A starting solution of Na₂SO₄ (25.01 g), MgSO₄ (as buffering agent—37.09g as MgSO₄.7H₂O) and NaHCO₃ (5 g) in 500 mL of water was made. Thissolution was heated to 70° C. To this initial mixture were added a 2.5%,by oxide weight, lime slurry (“Milk”). The lime slurry was a mixture ofhigh-calcium and dolomitic lime (90%/10% respectively). For each step inthe reaction, 5 mL of the lime slurry was added and then a 5 mL samplewas removed out of the reaction solution for ICP testing. The 5 mLsamples pulled from the reaction were filtered through a 0.45 pm syringefilter prior to running on the ICP. The ICP was calibrated with liquidcalibration standards.

The concentration of elements was calculated based on the diluting ofthe initial concentrations of the elements and the results are listed onFIG. 7 (composed of FIGS. 7A and 7B). Table 2 provides columndescriptions for the FIG. 7A columns. FIG. 7B columns correspond to theFIG. 7A columns. This diluting happened as a result of sampling and thelime slurry additions. FIG. 8 plots these

TABLE 2 Column Legend: A = Sample Number B = Sample Name C = Milk Added(ml) D = Milk Added Cumulative (ml) E = Sample Volume F = SolutionVolume G = Ca(OH)₂ Added (mg) H = pH I = Temperature (° C.) J = Ca(317.933) (mg/L) K = Mg (279.077) (mg/L) L = Mg observed (mg) M = Mgcalculated (mg) N = Na, raw data (mg/L) O = Na observed (mg) P = Nacalculated (mg) Q = S 180.669 (mg/L) R = S observed (mg) S = Scalculated (mg) T = S in CaSO₄ (mg of S)“calculated values” versus values observed in the ICP analysis, forsulfur. When the measured value for sulfur deviated from the calculatedvalue this was an indication that CaSO4 was forming in the solution.

During the experiment, the pH was being buffered at around pH 9 due tothe Mg²⁺ ions in solution. Once the Mg²⁺ ions were depleted, the pH wentup rapidly (see FIG. 9). FIG. 9 shows the amount of sulfur being removedfrom the aqueous portion of the reaction. The “S in CaSO₄” value wasderived by subtracting “observed sulfur” from the “calculated sulfur” ofFIG. 7. FIG. 9 also shows Mg²⁺ being depleted throughout the reaction.When Mg²⁺ is close to zero, the pH starts to climb rapidly. The Mg²⁺ wasdropping out of the solution as insoluble Mg(OH)₂. When there was nomore Mg²⁺ to absorb the OH-ions, the pH went up rapidly. Sulfur removalcontinued to climb as the pH was increasing; this was evidence that NaOHwas being generated.

Example 2

An experiment was conducted to illustrate calcium behavior in thepresence of NaHCO₃, a main component of trona. The NaHCO₃ reacted withCa²⁺ in the solution to produce CaCO₃, which is very insoluble. Theexperimental setup and results are shown in Table 3 and plotted in FIG.10. These experiments were conducted at 25° C. The same equipment usedin Example 1 was also used in Example 2.

TABLE 3 [NaHCO₃] = NaHCO₃ Sample Total Theoretical 4.6 g/100 mL NaHCO₃Effect on Taken Volume [Na] Measured Measured Measured NaHCO₃Cumulative, Ca²⁺ ions mL mL mg/L Ca mg/L Na mg/L pH Added (mL) mLInitial −5 495 0 713 40 12.45 0 0 Saturated lime +5 mL −5 495 124 568110 12.39 5 5 NaHCO₃ +10 mL −5 495 249 370 194 12.34 5 10 NaHCO₃ +15 mL−5 495 373 147 281 12.26 5 15 NaHCO₃ +20 mL −5 495 498 4 364 12.18 5 20NaHCO₃

Example 3

An experiment was conducted to illustrate calcium behavior in thepresence of K₂CO₃. The K₂CO₃ reacted with Ca²⁺ in the solution toproduce CaCO₃, which is very insoluble. The reaction is as follows:Ca²+(aq)+CO₃ ²⁻(aq)-->CaCO₃(s).

A saturated calcium hydroxide solution was made by adding excess CaO(High-Calcium Quicklime) to deionized water and then filtering to make aclear solution. Specifically, 4.0029 g of CaO was added to 500 mL ofwater, then filtered to get saturated Ca(OH)₂ water. 1.8475 g of K₂CO₃(reagent grade) was added to 200 mL of water. K₂CO₃ was then added to500 ml of the clear saturated lime solution to show that CO₃ from K₂CO₃would react with and drop calcium ions from the solution. The resultsare shown in Table 4 and depicted in FIG. 11. For each addition of K₂CO₃solution, the Ca²⁺ ion concentration was reduced, presumably due to Ca²⁺reacting with CO₃ to form CaCO₃. These experiments were conducted at 25°C. Unless specified otherwise, the same equipment and material sourcesused in Example 1 were also used in Example 3.

TABLE 4 K₂CO₃ K₂CO₃ Total sol'n sol'n Samp. sol'n K₂CO₃ K2+ C032− ICPICP ICP added cum. taken vol. added added added [Ca²⁺] [K²⁺] [CO₃ ²⁻] mlml ml ml pH mg mg mg mg/I mg/I mg/I 0.00 −10.00 490.00 12.44 0 0 0 813.80.3 6.9 10.00 10.00 −10.00 490.00 12.43 92 52 40 627.0 66.5 5.2 10.0020.00 −10.00 490.00 12.43 185 105 80 500.2 103.6 6.1 10.00 30.00 −10.00490.00 12.40 277 157 120 435.2 169.8 5.3 10.00 40.00 −10.00 490.00 12.39370 209 160 418.9 225.1 4.3 10.00 50.00 −10.00 490.00 12.39 462 261 201388.3 323.5 4.2 10.00 60.00 −10.00 490.00 12.38 554 314 241 350.0 374.04.7 10.00 70.00 −10.00 490.00 12.37 647 366 281 275.0 376.0 7.4 10.0080.00 −10.00 490.00 12.36 739 418 321 227.2 457.6 8.2 10.00 90.00 −10.00490.00 12.35 831 470 361 188.7 527.5 7.1 10.00 100.00 −10.00 490.0012.34 924 523 401 153.4 611.5 8.0 10.00 110.00 −10.00 490.00 12.33 1016575 441 102.6 637.0 10.8 10.00 120.00 −10.00 490.00 12.31 1109 627 48164.5 678.4 18.2 10.00 130.00 −10.00 490.00 12.30 1201 679 521 36.4 699.658.8 10.00 140.00 −10.00 490.00 12.29 1293 732 561 13.0 768.2 104.510.00 150.00 −10.00 490.00 12.27 1386 784 602 2.3 810.0 145.9

Example 4

An experiment was conducted to illustrate calcium behavior in thepresence of Li₂CO₃. The Li₂CO₃ reacted with Ca²⁺ in the solution toproduce CaCO₃, which is very insoluble. The reaction is as follows:Ca²⁺(aq)+CO₃ ²⁻(aq)-->CaCO₃(s).

A saturated calcium hydroxide solution was made by adding excess CaO(High-Calcium Quicklime) to deionized water and then filtering to make aclear solution. Specifically, 3.9835 g of CaO was added to 500 mL ofwater, then filtered to get saturated Ca(OH)₂ water. 5 g of Li₂CO₃(reagent grade) was added to 500 mL of water. Li₂CO₃ was then added to500 ml of the clear saturated lime solution to show that CO₃ from Li₂CO₃would react with and drop calcium ions from the solution. The resultsare shown in Table 5 and depicted in FIG. 12. For each addition ofLi₂CO₃ solution, the Ca²⁺ ion concentration was reduced, due to Ca²⁺reacting with CO₃ to form CaCO₃. These experiments were conducted at 25°C. Unless specified otherwise, the same equipment and material sourcesused in Example 1 were also used in Example 4.

TABLE 5 Li₂CO₃ Li₂CO₃ total sol'n sol'n samp. sol'n Li₂CO₃ Li²⁺ ICP ICPadded cum. taken vol. added added [Ca²⁺] [CO₃ ²⁻] ml ml ml ml pH mg mgmg/I mg/I 0.00 0 −10.00 490.00 12.50 0 0 849.8 3.6 10.00 10 −10.00490.00 12.51 100 19 764.0 6.4 10.00 20 −10.00 490.00 12.50 200 38 588.43.1 10.00 30 −10.00 490.00 12.49 300 56 421.8 7.2 10.00 40 −10.00 490.0012.47 400 75 278.9 6.6 10.00 50 −10.00 490.00 12.46 500 94 133.7 19.910.00 60 −10.00 490.00 12.42 600 113 23.7 104.1 10.00 70 −10.00 490.0012.39 700 131 1.4 189.7 10.00 80 −10.00 490.00 12.36 800 150 1.0 345.510.00 90 −10.00 490.00 12.33 900 169 1.0 429.6 10.00 100 −10.00 490.0012.31 1000 188 1.1 577.0 10.00 110 −10.00 490.00 12.28 1100 207 1.1811.0 10.00 120 −10.00 490.00 12.26 1200 225 1.1 799.9 10.00 130 −10.00490.00 12.23 1300 244 1.1 970.6 10.00 140 −10.00 490.00 12.21 1400 2631.2 1273.6 10.00 150 −10.00 490.00 12.19 1500 282 1.2 1301.7 10.00 160−10.00 490.00 12.18 1600 301 1.2 1511.7 10.00 170 −10.00 490.00 12.171700 319 1.2 1633.6 10.00 180 −10.00 490.00 12.15 1800 338 1.2 1609.510.00 190 −10.00 490.00 12.15 1900 357 1.2 1913.3 10.00 200 −10.00490.00 12.14 2000 376 1.3 2098.6

A higher concentration of carbonate ions was added in Example 4 ascompared to Example 3. The same reduction in calcium was achieved, butin fewer iterations.

The following equipment and reagents were used in Examples 5 and 6:

ICP Spectrometer; Perkin Elmer 7300V

pH Meter; Orion 920A+

100 mesh sieve

Anhydrous Magnesium Chloride; Reagent Grade

Sodium Sulfate; Reagent Grade

Sodium Bicarbonate (Arm & Hammer® baking soda)

Lime—Quicklime obtained from Graymont (PA) Inc. (Pleasant Gap, Pa.).

Masterflex Peristaltic pump, with 2.79 mm tygon tubing

Example 5

Experiments were conducted to prove the feasibility of the reactionbelow.Ca(OH)₂+MgSO₄(aq)→CaSO_(4(s))+Mg(OH)_(2(S))

MgCl₂ was used as our source of Mg²⁺ ions. It is expected that Mg²⁺ ionsfrom MgSO₄ would behave similarly as those from MgCl₂. Therefore, theMgCl₂ data is representative.

A solution was made containing 100 g/L NaSO₄ and MgCl₂. The secondsolution was a milk of lime solution (water and CaO); these twosolutions were mixed together to complete the following reaction.Ca(OH)₂+MgCl₂+Na₂SO₄→CaSO₄+Mg(OH)₂+NaCl₂

This experiment was repeated several times with varying MgCl₂concentrations according to Table 6. Pleasant Gap quicklime was used forall experiments. The quicklime was slaked and filtered through a 100mesh sieve. All experiments were run until the full 300 ml of eachreactant was used up. Liquid samples were analyzed to measure the sulfurreduction in the fluid stream. Sulfur removal was calculated based onthe difference between the mixed and final solutions (reduction insulfur=initial solution/2−final solution). A sample of initial stockNa₂SO₄ solution was analyzed for sulfur concentration. The mixedsolution was estimated by dividing initial concentration by 2, since themixed solution was a 1:1 mixture (by volume) of the lime solution andthe Na₂SO₄ solution. The final filtered solution was analyzed forsulfur.

For experiment 6, a lower pH of initial stock solution (Na₂SO₄/MgCl₂)was used. The initial pH was 8.73. 1.3 ml of 1N HCI was added to get topH 5.02, but this value was not stable and kept rising. Another 0.08 mlwas added and the pH dropped rapidly back down to below 5. Experiment 6was started at that point.

TABLE 6 Theoretical Conc. Needed Exp. Initial Mixed Initial MixedVolume, Actual Conc. Used No. Comp. Conc. Conc. Molar Molar ml CaONa₂SO₄ MgCl₂ 1 CaO(Lime) 78.86 g/L 39.43 g/L 1.408 0.704 300 24 g/ 60 g/0 g/ Na₂SO₄ 200 g/L 100 g/L 1.408 0.704 300 300 ml 300 ml 300 ml MgCl₂ 0g/L 0 g/L 0.000 0.000 300 2 CaO(Lime) 78.86 g/L 39.43 g/L 1.408 0.704300 24 g/ 60 g/ 20 g/ Na₂SO₄ 200 g/L 100 g/L 1.408 0.704 300 300 ml 300ml 300 ml MgCl₂ 66.64 g/L 33.32 g/L 0.700 0.350 300 3 CaO(Lime) 78.86g/L 39.43 g/L 1.408 0.704 300 24 g/ 60 g/ 42.2 g/ Na₂SO₄ 200 g/L 100 g/L1.408 0.704 300 300 ml 300 ml 300 ml MgCl₂ 133.28 g/L 66.64 g/L 1.4080.704 300 4 CaO(Lime) 78.86 g/L 39.43 g/L 1.408 0.704 300 39.86/ 100 g/16.66 g/ Na₂SO₄ 200 g/L 100 g/L 1.408 0.704 300 500 ml 500 ml 500 mlMgCl₂ 33.32 g/L 16.66 g/L 0.350 0.175 300 5 CaO(Lime) 78.86 g/L 39.43g/L 1.408 0.704 300 39.86/ 100 g/ 49.98 g/ Na₂SO₄ 200 g/L 100 g/L 1.4080.704 300 500 ml 500 ml 500 ml MgCl₂ 99.96 g/L 49.98 g/L 1.056 0.528 3006 CaO(Lime) 78.86 g/L 39.43 g/L 1.408 0.704 500 39 g/ 100 g/ 32.32 g/Na₂SO₄ 200 g/L 100 g/L 1.408 0.704 500 500 ml 500 ml 500 ml MgCl₂ 66.64g/L 33.32 g/L 0.700 0.350 500

For every mole of Mg added to the reaction, 1 mole of sulfur was removedfrom the solution. This data is depicted in the graph of FIG. 13.Experiments 1-5 are represented by the black dots. Experiment 6 isrepresented by the black square. In this graph, the x-axis representshow much Mg was in the initial NaSO₄/MgCl₂ solution. The y-axisrepresents how much sulfur was removed from the initial solution. Theexperiments confirm the feasibility of regeneration of Mg(OH)₂ fromMgSO₄ and the increase in sulfur removal efficiency in relation toincreased Mg ion concentration.

Example 6

In this experiment a potential pH range was determined for theregeneration reaction evaluated in Example 5. A solution of NaHCO₃ (0.28g/500 ml), Na₂SO₄ (2 g/500 ml) and MgCl₂ (1.28 g/500 ml) giving a pH of8.12 was started with. Powdered Ca(OH)₂ was then added to this solutionin 0.25 g increments and the pH was plotted against the addition ofCa(OH)₂. The results obtained are depicted in FIG. 14. The Mg ionsbuffered the solution to about pH 10-11. Once the Mg ions were depleted,the pH quickly went to 12.5. Presumably, at pH 12.5 calcium from Ca(OH)₂was no longer able to go into solution and the sulfur removal stopped.Sulfur removal was not measured in this experiment.

Without further elaboration, it is believed that one skilled in the artcan use the preceding description to utilize the present disclosure toits fullest extent. The examples and embodiments disclosed herein are tobe construed as merely illustrative and exemplary and not a limitationof the scope of the present disclosure in any way. It will be apparentto those having skill in the art, and having the benefit of thisdisclosure, that changes may be made to the details of theabove-described embodiments without departing from the underlyingprinciples of the disclosure herein.

The invention claimed is:
 1. A system for regenerating an alkali processstream, comprising: a first separator configured to separate a supplystream from one or more supply vessels into at least a first stream; acarbonate supply configured to supply carbonates; a mixer downstream ofthe first separator and the carbonate supply, the mixer configured toreceive the carbonates and the first stream and provide a mixed solutioncomprising calcium carbonate and sodium hydroxide; and a secondseparator downstream of the mixer, the second separator configured to(a) remove at least a portion of the calcium carbonate from the mixedsolution, (b) recycle at least a portion of the sodium hydroxide to atleast one of the one or more supply vessels, or (c) remove at least aportion of the calcium carbonate from the mixed solution, and recycle atleast a portion of the sodium hydroxide to at least one of the one ormore supply vessels.
 2. The system of claim 1, wherein the firstseparator is configured to separate the supply stream into at least thefirst stream and a second stream comprising calcium sulfate.
 3. Thesystem of claim 2, further comprising a recycle line in fluidcommunication with the first separator and at least one of the one ormore supply vessels, wherein at least a portion of the calcium sulfateof the second stream is recycled to the at least one of the one or moresupply vessels via the recycle line.
 4. The system of claim 1, whereinthe second separator is configured to (a) remove at least a portion ofthe calcium carbonate from the mixed solution, and (b) recycle at leasta portion of the sodium hydroxide to at least one of the one or moresupply vessels.
 5. The system of claim 1, wherein the second separatoris configured to remove at least a portion of the calcium carbonate fromthe mixed solution, wherein a first portion of the removed calciumcarbonate is recycled to the carbonate supply and a second portion ofthe removed calcium carbonate is directed to a location other than thecarbonate supply.
 6. The system of claim 1, wherein the mixer is a firstmixer, and wherein the one or more supply vessels include: a lime supplyvessel comprising lime; and a second mixer configured to mix the limefrom the lime supply vessel with a liquid stream comprising sodiumsulfate to produce the supply stream.
 7. The system of claim 1, whereinthe mixer is a first mixer, and wherein the one or more supply vesselsinclude: a lime supply vessel comprising lime; a third separatorconfigured to separate a stream comprising ore into a liquid streamcomprising sodium sulfate and an oxidized ore stream; and a second mixerconfigured to mix the lime from the lime supply vessel with the sodiumsulfate from the liquid stream to produce the supply stream.
 8. Thesystem of claim 1, wherein the mixer is a first mixer, and wherein theone or more supply vessels include: an ore supply vessel comprising anore supply; an oxidizing agent vessel comprising an oxidizing agent; anoxidizer vessel downstream of the ore supply vessel and the oxidizingagent vessel, wherein the oxidizer vessel is configured to (a) receivethe ore supply and the oxidizing agent, and (b) produce an oxidizedsupply; a third separator downstream of the oxidizer vessel andconfigured to separate the oxidized supply into a liquid streamcomprising sodium sulfate and an oxidized ore stream; a lime supplyvessel comprising lime; and a second mixer downstream of the thirdseparator and the lime supply vessel, wherein the second mixer isconfigured to receive the lime and the sodium sulfate to produce thesupply stream.
 9. The system of claim 1, further comprising: a recyclestream in fluid communication with the second separator; and a pHmodifier vessel comprising a pH modifier feed and in fluid communicationwith the recycle stream, wherein the portion of the sodium hydroxide isrecycled to the pH modifier vessel via the recycle stream.
 10. Thesystem of claim 1, wherein the carbonates include at least one of sodiumcarbonate, sodium bicarbonate, trisodium hydrogendicarbonate dihydrate,magnesium carbonate, potassium carbonate, potassium bicarbonate, lithiumcarbonate or lithium bicarbonate.